1. Field of the Invention
The present invention relates to a color correction apparatus, a color correction controller, and a color correction system, for performing color adjustment among imaging apparatus.
2. Description of the Related Art
In video cameras for use in broadcast stations, it is required that the color characteristics of each video camera (hereinafter referred to simply as a camera) be precisely adjusted. However, in imaging apparatus such as cameras for use in broadcast stations, a difference in the output image among cameras can occur due to slight variations in spectral characteristics of color filters or color separation prisms disposed in front of an image sensor device such as a CCD (charge coupled device). To avoid the above problem, the inventors of the present invention have proposed a technique of making color adjustment for each camera using a linear matrix circuit which is generally disposed in the camera for use in broadcast stations. The linear matrix circuit serves to electronically compensate for an error in the color of the reproduced image caused by the difference in the spectral characteristic between a camera and the ideal spectral characteristic for example according to the NTSC standard. In this technique of compensating for the color difference among cameras using the linear matrix circuit, the same colors for example colors of a color chart are measured by two different imaging apparatus, and the coefficients of the linear matrix circuit are determined by means of calculation based on the data of the colors so that the differences in the colors between the two imaging apparatus are minimized. The resultant coefficients are given to the linear matrix circuit.
The color adjustment process using the linear matrix circuit is briefly described below. The linear matrix circuit performs a matrix calculation according to the following equation (1).
Ro=Ri+axc3x97(Rixe2x88x92Gi)+bxc3x97(Rixe2x88x92Bi)
Go=Gi+cxc3x97(Gixe2x88x92Ri)+dxc3x97(Gixe2x88x92Bi)
Bo=Bi+exc3x97(Bixe2x88x92Ri)+fxc3x97(Bixe2x88x92Gi)xe2x80x83xe2x80x83(1)
where Ri, Gi, and Bi are red, green, and blue signals which are input to the linear matrix circuit, Ro, Go, and Bo are red, green, and blue signal which are output from the linear matrix circuit, and a-f are coefficients which are determined such that the color difference among cameras is minimized.
The color adjustment process is performed as follows. The image of a particular color of a color chart such as Macbeth Color Chart (trade name) is taken by each camera which is to be adjusted, and the levels of the obtained R, C, and B signals are detected. This process is performed repeatedly for a plurality of desired colors. The levels of the R, G, and B signals detected by a reference camera are substituted into Ro, Go, and Bo, respectively, of equation (1), for each color. The levels of the R, G. and B signals detected by a camera which is to be adjusted relative to the reference camera are substituted into Ri, Gi, and Bi, respectively, of equation (1), for each color. Then the coefficients a-f are calculated.
In the above color adjustment method using the linear matrix circuit, when the color adjustment is performed for two colors, it is possible to uniquely determine the coefficients a-f so that the two cameras have the same characteristics for the selected two colors. However, in the case where the color adjustment is performed for three or more colors, it is generally impossible to uniquely determine the coefficients a-f. In this case, the coefficients a-f are determined such that the sum of squared errors of the respective colors among cameras is minimized using for example the least squares method. This means that it is difficult to eliminate the difference for all colors among cameras although it is possible to approximately make adjustment for a plurality of colors.
In view of the above problem in the conventional technique, it is an object of the present invention to provide a color correction apparatus, color correction controller, and color correction system, capable of making color adjustment among imaging apparatus for a great number of colors.
According to a first aspect of the invention, there is provided a color correction apparatus for use in an imaging apparatus, the imaging apparatus including imaging means for sensing the image of a subject and generating a signal including information about the colors of the subject, the color correction apparatus comprising:
color representation data generating means for generating color representation data representing colors, in accordance with the signal generated by the imaging means in the image sensing operation; and
correction means which divides the color space in which the color representation data is represented in coordinates of the color space into a plurality of regions, and corrects the color representation data generated by the color representation data generating means, in accordance with a procedure determined for each region of the color space thereby adjusting a color represented by the signal generated by the imaging means with respect to a reference color.
According to a second aspect of the present invention, there is provided a color correction controller for controlling correction means provided in an imaging apparatus, the imaging apparatus comprising:
imaging means for sensing the image of a subject and generating a signal including information about the colors of the subject;
color representation data generating means for generating color representation data representing colors, in accordance with the signal generated by the imaging means in the image sensing operation; and
the correction means which divides the color space in which the color representation data is represented in coordinates of the color space into a plurality of regions, and corrects the color representation data generated by the color representation data generating means, in accordance with a procedure determined for each region of the color space thereby adjusting a color represented by the signal generated by the imaging means with respect to a reference color;
the color correction controller comprising procedure determining means for determining the procedure of dividing the color space into the plurality of regions corresponding to a plurality of particular colors, and determining a correction procedure performed by the correction means for each region, in accordance with the signal which is generated by the imaging means when sensing the plurality of particular colors and also in accordance with the information representing references for the plurality of particular colors, so that the color correction controller controls the correction means in accordance with the correction procedure determined.
According to a third aspect of the present invention, there is provided a color correction system for use with an imaging apparatus, the imaging apparatus including imaging means for sensing the image of a subject and generating a signal including information about the colors of the subject, the color correction system comprising:
color representation data generating means for generating color representation data representing colors, in accordance with the signal generated by the imaging means in the image sensing operation;
correction means which divides the color space in which the color representation data is represented in coordinates of the color space into a plurality of regions, and corrects the color representation data generated by the color representation data generating means, in accordance with a procedure determined for each region of the color space thereby adjusting a color represented by the signal generated by the imaging means with respect to a reference color; and
procedure determining means for determining the procedure of dividing the color space into the plurality of regions corresponding to a plurality of particular colors, and determining a correction procedure performed by the correction means for each region, in accordance with the signal which is generated by the imaging means when sensing the plurality of particular colors and also in accordance with the information representing references for the plurality of particular colors, so that the color correction controller controls the correction means in accordance with the correction procedure determined.
In the color correction apparatus according to the first aspect of the present invention, the color representation data generating means generates color representation data representing colors in accordance with the signal generated by the imaging means, and correction means corrects the color representation data in accordance with the correction procedure determined for each region in the color space so that the colors represented by the signal generated by the imaging means is adjusted with respect to the reference colors.
In the color correction controller according to the second aspect of the present invention, for each region in the color space corresponding to the plurality of particular colors, the procedure determining means determines the correction procedure performed by the correction means of the imaging apparatus, in accordance with the signal which is generated by the imaging means when sensing the plurality of particular colors and also in accordance with the information representing references for the plurality of particular colors, whereby the color correction controller controls the correction means in accordance with the correction procedure determined.
In the color correction system according to the third aspect of the present invention, the procedure determining means determines, for each region in the color space corresponding to the plurality of particular colors, the correction procedure performed by the correction means of the imaging apparatus, in accordance with the signal which is generated by the imaging means when sensing the plurality of particular colors and also in accordance with the information representing references for the plurality of particular colors, the color representation data generating means generates color representation data representing colors in accordance with the signal generated by the imaging means, and correction means corrects the color representation data in accordance with the correction procedure determined for each region in the color space so that the colors represented by the signal generated by the imaging means is adjusted with respect to the reference colors.